The chicken is the latest animal to have its genetic sequence decoded.

A team led by the Washington University School of Medicine, St Louis, has read through the DNA of the red jungle fowl, the ancestor of domestic chickens.

The genetic variations of three types of domestic chickens have also been mapped by an international team at China's Beijing Genomics Institute.

The work will be useful for scientists as they probe the causes of disease and could help them combat avian flu.

The chicken genome comprises about one billion base pairs, or "letters", of DNA - in contrast to the three billion found in humans.

More work required

Hidden in the chicken DNA code are its genes, the starting templates the bird's cells use to make proteins.

It is these sophisticated molecules that build and maintain the animal's body.

The sequence deposited in a public database this week represents a first draft. It still needs to be tidied up and the gene locations tracked down.

Nonetheless the code will already provide invaluable information for biomedical and agricultural researchers around the globe.

Dr Dave Burt, of the Roslin Institute, UK, has been working on chicken genomics for about 10 years.

He said the completion of the sequencing effort, which had cost $13m, was most welcome.

"The basic scaffold is there. Now we have to attach the meaning to it - it needs people to annotate the sequence, to say where the genes are," he said.

"The project will bring together all the biological knowledge about the chicken."

Scientists will compare the data with the human code to see if there is information there that can throw light on our own biochemical make-up.

Ideal model

Recent outbreaks of avian flu have accelerated researchers' interest in learning more about the chicken genome and how genetic variation may play a role in the susceptibility of different strains to the disease.

In addition to its tremendous economic value as a source of eggs and meat, the chicken (Gallus gallus) is widely used in biomedical research.

It serves as an important model for the study of embryology and development, as well as for research into the connection between viruses and some types of cancer.

The Washington University researchers, directed by Dr Richard Wilson, deposited the initial assembly into the GenBank database for worldwide release.

The draft has been used by a team, led by the Beijing Genomics Institute in China and supported by the Wellcome Trust in Britain, to create a map of genetic variation for three different strains of domestic chickens.

Production pointers

The strains were a broiler strain from the United Kingdom, a layer strain from Sweden and a Silkie strain from China.

To make the map, researchers identified and analysed about two million genetic variation sites, mostly single nucleotide polymorphisms (SNPs).

SNPs are minute variations scattered through the DNA sequence and make a major contribution to the differences between individual animals in a species.

"We can use this knowledge of genetic variation to map characteristics that could be production traits, such as how fast they grow," said Dr Burt.